1. Field of Invention
The present invention relates to nuclear technique for detecting impurities such as salt water and sulfur in petroleum refining and producing operations.
2. Description of Prior Art
Petroleum products often contain small concentrations of undesirable impurities, such as chlorine, sulfur and other elements. For example, even relatively small concentrations of salt water in crude oil can often cause major problems during refining operations. The amount of sulfur in petroleum or fuel oil must be closely monitored for processing and environmental reasons.
A recent article in Analytical Chemistry, Volume 46, Number 9, August, 1974, page 1223 and following, deals with determining the amount of sulfur in oil using neutron capture gamma ray spectroscopy. However, it has been found with the present invention that for crude oil of varying and unknown chlorine content, the sulfur readings are varied due to the varying chlorine content. The isotope .sup.32 S, upon capture of thermal neutrons, emits relatively low intensity 8.64, 7.78, 7.42, 7.19, 6.64 and 5.97 MeV gamma radiation in addition to the relatively intense 5.42 MeV radiation. The isotope .sup.35 Cl, upon capture of thermal neutrons, emits 7.79, 7.42, 6.64 and 6.11 MeV gamma radiation. The second and first escape peaks of the 6.64 and 6.11 MeV chlorine capture gamma radiation fall at energies 5.62 and 5.60 MeV, respectively. These escape peaks essentially overlap the primary sulfur capture peak at 5.43 MeV. Due to these overlapping energy peaks, unless the chlorine level in a sample were known and constant, sulfur readings obtained with this prior art technique were not accurate. However, the salt water (and thus chlorine) content of crude oil varies from well to well as well as during the production life of a well for a number of reasons. So far as is known, the only way prior to the present invention to determine chlorine content of crude oil was by chemical analysis.